The major emphasis of this research program will be focused on further elucidating the ocular physiology of the teleost. Preliminary results indicate that carbonic anhydrase is an essential component of the counter current oxygen multiplier found in the teleost choroid, consisting of a rete mirabile. The anatomical description of these vessels and the histochemical localization of carbonic anhydrase within them will be determined and correlated with our hypothesis of counter current oxygen multiplication. The presence of an anatomical exchanger suggests the possibility that other components, such as thermal energy, may also be localized at the retinal surface. In pursuit of this hypothesis, three-dimensional temperature profiles will be determined with particualr emphasis in the region and the rete. Measurements of thermal conductivity, direct calorimetry and solar radiation absorption will be used in evaluating the role of the rete in counter current heat exchange. Using the electroretinogram as a sensitive indicator of retinal integrity, the influence of hyperbaric oxygen tensions on the teleost and other vertebrate retinas will be investigated. Preliminary results indicate that the teleost retina is resistant to oxygen toxicity, whereas, amphibian and mammalian retinas exhibit profound changes in their metabolic pathways and electroretinograms upon exposure to hyperoxic conditions. The distribution of oxygen throughout the eye will be investigated using micro oxygen polarographic electrodes. Studies will continue on the influence of near ultra violet radiation as the causative agent in the high occurence of cataracts (lenticular lesions) in hatchery reared trout exposed to sunlight.